1. Field of the Invention
The present invention relates to wireless communication and more particularly, a method and apparatus for converting a mode for client cooperation in a wireless communication system.
2. Related Art
In next generation multimedia mobile communication systems, which have been actively studied in recent years, there is a demand for a system capable of processing and transmitting a variety of information (e.g., video and radio data) in addition to the early-stage voice service. Further, a 3rd generation wireless communication system is followed by a 4th generation wireless communication which is currently being developed aiming at supporting a high-speed data service of 1 gigabits per second (Gbps) in downlink and 500 megabits per second (Mbps) in uplink. The wireless communication system is designed for the purpose of providing reliable communication to a plurality of users irrespective of their locations and mobility. However, a wireless channel has an abnormal characteristic such as a fading phenomenon caused by a path loss, noise, and multipath, an inter-symbol interference (ISI), a Doppler effect caused by mobility of a user equipment, etc. Therefore, various techniques have been developed to overcome the abnormal characteristic of the wireless channel and to increase reliability of wireless communication.
Meanwhile, with the advent of a ubiquitous environment, there is a rapid increase in a demand for receiving a seamless service anytime anywhere by using equipments. In order to satisfy such a demand, a client cooperation technique may be introduced in a wireless communication system. The client cooperation technique refers to a technique by which a specific device helps transmission of another device. That is, one device may directly communicate with a base station (BS) or may indirectly communication with the BS by the aid of another device. The client cooperation technique has an effect of lower power consumption, throughput enhancement, etc.
The client cooperation technique can be more effectively used in a multi-radio access technology (RAT) device. The multi-RAT device refers to a device that can operate in a plurality of communication systems. For example, the multi-RAT device can operate both in institute of electrical and electronics engineers (IEEE) 802.16m and IEEE 802.11. To provide an easiness access to the BS anytime anywhere and to maintain effective performance, the multi-RAT device can use a multi-RAT client cooperation technique (i.e., improved tethering) in a heterogeneous network.
A multi-RAT device performing a client cooperation technology may require searching for a different multi-RAT device which can help performing client cooperation. Therefore an efficient device search method is required for a multi-RAT device to perform the client cooperation technology without any support.